In this paper, we investigate the trust-based mechanisms underlying the relationship between ethical leadership and followers? organisational citizenship behaviours (OCBs). Based on three-wave survey data obtained from 184 employees and their supervisors, we find that ethical leadership leads to higher levels of both affective and cognitive trust. In addition, we find support for a three-path mediational model, where cognitive trust and affective trust, in turn, mediate the relationship between ethical leadership and follower OCBs. That is to say, we found that ethical leadership leads to the development of cognitive trust, which subsequently influences the development of affective trust. Affective trust, in turn, induces followers to exhibit OCBs as a means of reciprocating the leader?s favourable behaviour. Our findings suggest that both affective and cognitive trust plays an important role in the social exchange processes that underlie the relationship between ethical leadership and the discretionary behaviour of followers.